Polymorphism of Beta-Lactoglobulin Coding and 5′-Flanking Regions and Association with Milk Production Traits

ABSTRACT

Beta-lactoglobulin (LGB) is a major whey protein expressed in the milk of ruminants and has two dominant alleles A and B. It has been reported that alleles in the coding region are connected with distinct promoter variants and might influence the quality and quantity of milk and the cheese making process. The aim of this study was to detect genetic polymorphisms of the coding and 5'-flanking regions of LGB and its association with milk production. Pyrosequencing and PCR-RFLP were utilized to estimate the allele frequency at positions X63139:g.435 C>G, g.424 T>G, g.422G>A and coding region at codon 64, in three native breeds (Mazandarani, Sarabi and Golpaygani) and Holstein cattle of Iran. There were different allele frequencies and haplotype patterns in each breed. A linkage disequilibrium was observed between polymorphisms at codon 64 and polymorphisms at 5'-flanking region of promoters. The results showed that the CC genotype at g.435 C>G had significant effect on milk and fat yield in Holstein and on milk yield in Golpaygani breeds. The AG and GG genotypes at g.422G>A position were associated with milk yield in Holstein and Golpaygani, respectively. Although LGB genotypes had no significant effect on fat yield of Holstein, the LGB*AB tended to produce higher fat yield than the BB genotype. The existence of additional haplotypes could be expected and were shown in this study.

Keywords:

• single-nucleotide polymorphism
• beta-lactoglobulin